Preload is the adjustment that the motorcycle owner should use to set his/her sag.
Sag is the distance the bike settles into after the bike is loaded(rider, 2up, gear).
Proper sag for normal street riding is correctly set at 25% of your travel. 20% for more agressive riding(as it was explained to me).
If you have a 12" shock with about 2" of travel the preload should be set so that the bike sinks about 1/2" when the rider sits on it. To properly set this you will need a helping hand, and a yardstick or tape measure.
With bike upright bounce up and down a couple of time to besure the shock is not hung up at all. Now have your helper measure from the ground to a fixed point(like the bottom of the fender). You are straddling the bike upright at this point but not putting any weight on it. Now sit down. Measure. Set the preload either more or less firm till you have around 20-25% of your shocks travel measured. Your preload is now set and the shock will be able to do the job it was designed to... So are you bottoming out, shock too firm and poor ride? If so, the shock is simply not set up correctly for your weight and riding style. If you have 11" shocks with a measly 1.46" of travel some bottoming out will occur on larger bumps. If you are setting your preload up as firm as possible to avoid bottoming out, you may be setting the bike up incorrectly and the shock cannot do it job the way it was designed. Anyways this is how ro properly use the preload on your rear shocks. Sag is also set in the front as well by adjusting the length of the PVC spacer till the front sags 20-25% as well. The bike will ride and handle the best with both the front and rear having the same amount of sag. for standard street riding.
sag also needs to be corrected when adding a 2nd passenger. the rear shocks will hold most the passenger weight and the front will almost remain the same as solo so only the rear need to be corrected.

Setting sag with a stock suspension or some progressive models can often be very difficult to get correct. This is due to the shock having 5 predetermined points set by the shock mfg. A screw down preload is best here where you should be able to set up the shocks to the exact sag you want.(provide of course the load is not too heavy or light)
The progressive 430 and works performance(and other high end shocks) utilize this system of preload setting.

 

Thanks rounder...that's good info to know! This will be saved in my favorites!

 

I'll keep doing SWAG's on my sags, nice write up.

 

20% is the setup for racing on smooth surfaces.One reason you want sag is so the wheel can drop into holes ir dips without loosing contact with the road.

 

Sag is easy. Too bad it costs an arm and a leg to get a shock that has compression and rebound damping. THAT'S a nice shock!!





Mike

 

Thank you. I was just thinking about this very same topic today.

 

Great info, Thanx for sharing

Merry Christmas !!!

 

Thanks for the reminder Rounder. Yes the Progressives are fine shocks, what a vast improvement over the stockers. And for sure Merry Christmas ! These are Progressive 440's / 12.5 inch length. Stock on the Fat Bob is 12 inch.

 

Not to go too far off topic, but what is the length of the std shocks on an 09 FXD?

 

With a tape measure, from the top bolt to the bottom bolt will give you the answer.